Has PHP stopped my audio files from playing?

I develop a site that contains hundreds of audio recordings of a Vedanta teacher's classes (the vast majority of which require a login although some are freely available as samples) and recently introduced PHP includes to practically every page, which of course meant changing .html file endings to .php.

All classes pages present a user with the option either to download the selected audio or play it online.

Since the change to 'php includes' clicking the Play Now link initiates only a download, not playing. I can think of no other change that might have caused this very recent behaviour.

I should add that I have no trouble playing or downloading the files, but then I have admin access and develop the site using Dreamweaver CS6 on a Mac. Yesterday a user (also a Mac user) said he gets an error message telling him he needs admin access for "that part of the site". He definitely has all the login info he needs (but of course not admin access) and has previously used that area of the site (via login) happily and successfully many, many times. However, on checking the public (non-login) page arshavidya(dot)org(dot)uk/downloads(dot)php on a PC running XP, the problem occurs there too, so login and platform appear not to be part of the problem.

Is the cause due to changing file endings to php? If so, what is the fix, please?

My sincere apologies for wasting your time, but it seems I was using a faultily set up version of IE 8. Having now tried several browsers, it works fine. Sorry again for not checking more carefully before rushing into the forum.